Froth flotation is a widely used process for selectively separating hydrophobic materials from non-hydrophobic materials in a mixture. It is particularly useful in separating fine solids from other solids in a liquid mixture by the selective attachment of hydrophobic solid particles to gas bubbles contained in the liquid mixture. Most often the gas used is air, which has been passed through the liquid mixture at such a rate to provide a sustained “froth” or accumulation of bubbles at the liquid-surface interface. The density difference between the gas bubbles and liquid provides the attached hydrophobic solid particles with buoyancy lifting these particles to the surface and leaving the non-hydrophobic solid particles behind in the bulk liquid mixture. The hydrophobic solid particles at the surface may then be separated from the bulk liquid mixture by draining the bulk liquid mixture or by mechanically skimming the surface.
In order to enhance separating efficiency, a “frother” or “frothing agent” is used to stabilize the gas bubbles carrying the hydrophobic solid particles to the surface. Frother's typically contain both polar and non-polar components. The non-polar or hydrophobic moiety will orient itself into the air phase while the polar or hydrophilic moiety will tend to orient itself into the liquid phase. The result is enhanced bubble wall strength and stability due to a localized increase in surface tension which allows the bubbles to hold and concentrate the desired hydrophobic material.
Effective frothers usually contain at least five (5) carbon atoms in a straight or branched chain configuration. Examples include 2-ethyl-3-hexanol, cyclic alcohols (for example pine oil), 1,1,3-triethoxy butane and polyalkylene glycols.
One of the most commonly used frothers is 4-methyl-2-pentanol or “MIBC”. MIBC, which displays excellent surface behavior and solubility, has been widely adopted in coal, metal and non-metal flotation processes due to its relatively low cost and good performance, especially in applications where minerals are relatively hydrophobic and readily floatable. However, MIBC is highly flammable, and therefore requires special care when being handled, transported and stored in large volumes. Accordingly, it is highly desirable to develop alternative frothers having improved flammability characteristics which can be used in place of MIBC in flotation processes in various industries, such as in the coal, mining, chemical, sewage and waste treatment industries.